Water vapor is employed in many applications, for example for cleaning and/or sterilizing or disinfecting containers for beverages. It is often necessary to ensure and document that the water vapor supplied with predetermined parameters, for example pressure and temperature, reaches the respective point with these predetermined parameters and has the desired effect at this point. For example, during the sterilization, disinfection and cleaning of containers for beverages, it has to be ensured that the desired effect is achieved at the treated objects, that means, for example, that the supplied water vapor with the predetermined temperature and/or the predetermined pressure also results in the desired heating of the container, but that the effect is not strong enough to cause any damage. This is, for example, particularly problematic if plastic bottles, for example PET bottles, are sterilized or disinfected with water vapor, as an unintended, stronger or longer heating very quickly leads to shrinkage or deformation of the plastics, thus making the containers useless. With these sensitive containers, a timed water vapor supply has proven of value, where the actual treatment duration is only extremely short and lasts, for example, from 0.5 to maximally 2 seconds.
In the past, many attempts have been made to develop devices which are intended to deter mine as quickly and precisely as required whether the treatment with water vapor has been sufficient.
For example, the DE 10 2006 023 764 describes a method and a device for sterilizing bottles or similar containers, where the temperature of the respective treated container is determined by at least one temperature sensor. This temperature must be determined at the end of the treatment section and at each container, so that errors are only recognized when the treatment is terminated, so that all containers that are being treated at this point in time must be rejected. The determination of the temperature is accomplished without contact by means of a pyrometer. While this method is very fast, it is susceptible to failures and very error-prone, in particular if the washing of the container is to be detected internally, while the container is simultaneously being washed with a fluid having the same or a similar temperature externally. In this situation, the temperature contrast is no longer sufficient for the pyrometer to detect the heat penetrating from the interior to the exterior of the container due to heat conduction. In case of an additional external washing process, the value that can be detected externally possibly greatly varies from the value at the inner surface.
Another device for monitoring the thermal treatment of bottles or the like is known from DE 44 27 570. This device contains a detector that can determine whether any sterilization fluid is present in the container by means of fluid measurement. To this end, a mist detector is employed which determines the density of the mist generated inside the container by the sterilization medium.